Fix unforged L1UserTxs query in forgeBatch

Previously the code was only querying the unforged L1UserTxs of a particular
queue, but this was incorrect because there are always two non-forged queues:
the frozen one and the open one.

Replace it by a query to all the unforged L1UserTxs via a new HistoryDB method.

db/historydb/historydb.go

@@ -763,6 +763,16 @@ func (hdb *HistoryDB) GetUnforgedL1UserTxs(toForgeL1TxsNum int64) ([]common.L1Tx
 	return db.SlicePtrsToSlice(txs).([]common.L1Tx), tracerr.Wrap(err)
 }
 
+// GetUnforgedL1UserTxsCount returns the count of unforged L1Txs (either in
+// open or frozen queues that are not yet forged)
+func (hdb *HistoryDB) GetUnforgedL1UserTxsCount() (int, error) {
+	row := hdb.dbRead.QueryRow(
+		`SELECT COUNT(*) FROM tx WHERE batch_num IS NULL;`,
+	)
+	var count int
+	return count, tracerr.Wrap(row.Scan(&count))
+}
+
 // TODO: Think about chaning all the queries that return a last value, to queries that return the next valid value.
 
 // GetLastTxsPosition for a given to_forge_l1_txs_num

db/historydb/historydb_test.go

@@ -720,6 +720,10 @@ func TestGetUnforgedL1UserTxs(t *testing.T) {
 	assert.Equal(t, 5, len(l1UserTxs))
 	assert.Equal(t, blocks[0].Rollup.L1UserTxs, l1UserTxs)
 
+	count, err := historyDB.GetUnforgedL1UserTxsCount()
+	require.NoError(t, err)
+	assert.Equal(t, 5, count)
+
 	// No l1UserTxs for this toForgeL1TxsNum
 	l1UserTxs, err = historyDB.GetUnforgedL1UserTxs(2)
 	require.NoError(t, err)